Cole crops (Brassica oleracea plants) are widely grown in many parts of the world. Such crops include cabbage (subspecies capitata), Savoy cabbage (subspecies sabauda), cauliflower (subspecies botrytis), broccoli (subspecies italica), curly kale (subspecies fimbriata), collard (subspecies acephala), kohl-rabi (subspecies gonoyloides), Brussels sprouts (subspecies gemmifera), Chinese kale (subspecies alboglabra), etc. The grower of the cole crop commonly purchases seed to produce the same or small immature plants which are transplanted.
The presence of weeds in the same planting area with the cole crop often has added significantly to the cost of production. For instance, hand-hoeing or mechanized cultivation frequently has been required to minimize competition from unwanted broadleaf weeds and grasses. Such a weed problem has been the most acute if the grower attempts to produce the cole crop from seeds as opposed to the growing of transplanted small plants. Unchecked weeds can lessen the ultimate cole crop yield, and in some instances will reduce the quality of the product through unavoidable contamination.
Heretofore the use of herbicides to control weeds growing among cole crops has met with only limited success. For instance, the use of compounds such as trifluralin and chlorthaldimethyl do not begin to adequately control the weed problem which commonly is encountered. Presently, weeds such as hairy gallinsoga, black nightshade and the wild mustards are costing cole crop producers large sums in hand-hoeing costs. Also, the commercial development of new herbicides is proving to be extremely expensive in view of the long testing and clearance requirements commonly imposed by governmental agencies. Such expense commonly cannot be justified for low-acreage crops including the cole crops. Also, some chemical herbicides formerly available for weed control in cole crops have been removed from the market, further exasperating the situation.
Heretofore cole crops (i.e., Brassica oleracea) have exhibited an absence of tolerance to triazine herbicides which has heretofore precluded the usage of such herbicides in an attempt to oontrol weeds which regularly appear in the planting area. Also, since triazines commonly are used as a herbicide with corn, residual amounts of the same in the soil commonly have had an adverse impact on a subsequently grown cole crop when one carries out crop rotation.
Cytoplasmically inherited triazine resistance previously has been available in Brassica campestris and B. napus. See in this regard, "Transfer of Cytoplasmically-Inherited Triazine Resistance From Bird's Rape to Cultivated Oilseed Rape (Brassica campestris and B. napus)", by W. D. Beversdorf, J. Weiss-Lerman, L. R. Erickson and V. Souza Machado appearing in the Canadian Journal of Genetics and Cytology, 22, Pages 167-172, June 1980. See also, "Uniparental Inheritance of Chloroplast Atrazine Tolerance in Brassica Campestris" by V. Souza Machado, J. D. Bandeen, G. R. Stephenson and P. Lavigne, Can. J. Plant Sci. 58:977-981, 1978. See also, U.S. Pat. No. 4,517,763 and copending U.S. patent application Ser. No. 797,916, filed Nov. 14, 1985 (now U.S. Pat. No. 4,658,085), which describe such herbicide tolerance in rape (i.e., Brassic napus) when combined with cytoplasmic male sterility, and the use of plants which possess such tolerance in improved hybridization processes. The desirability of also transferring such triazine tolerance to Brassica oleracea cole crops has heretofore been recognized by plant scientists to be a worthy objective and to possibly be within the realm of theoretical possibility if a way could be found to overcome significant problems inherent in this breeding approach.
The barriers to this interspecific hybridization heretofore have been regarded to be varied and complex. For instance, interspecific crosses of Brassica oleracea with B. campestris or B. napus previously have been recognized by plant scientists to be at best extremely difficult to achieve. Commonly the embryo resulting from the cross will abort. In those rare instances when the cross-pollination has produced an offspring, there has been no assurance that the offspring will be fertile and that it will be possible to backcross it to the recurrent parent (i.e., Brassica oleracea) and return to the normal 18 chromosome complement of Brassica oleracea. Brassica campestris has 20 chromosomes and Brassica napus has 38 chromosomes. See, for instance, the following technical articles:
U, N., 1935. Genome-analysis in Brassica with special reference to the experimental formation of B. napus and peculiar mode of fertilization. Jap. J. Bot. 7: 389-452. PA1 Calder, R. A., 1937. Interpollination of Brassicas. New Zeal. J. of Agric. 55: 299-308. PA1 Yarnell, S. H., 1956. Cytogenetics of the vegetable crops. II. Crucifers. Bot. Rev. 22: 81-166. PA1 Honma, S. and W. L. Summers, 1976. Interspecific hybridization between Brassica napus L. (Napobrassica group) and B. oleracea L. (Botrytis group). J. Amer. Soc. Hort. Sci. 101: 299-302. PA1 Chiang, M. S., B. Y. Chiang and W. F. Grant, 1977. Transfer of resistance to race 2 of Plasmodiophora brassicae from Brassica napus to cabbage (B. oleracea var. capitata). I. Interspecific hybridization between B. napus and B. oleracea var. capitata. Euphytica 26: 319-336. PA1 McNaughton, I. H. and C. L. Ross, 1978. Interspecific and inter-generic hybridization in the Brassicae with special emphasis on the improvement of forage crops. Ann. Rep. of the Scot. Plant Breed. Sta. 1978: 75-110. PA1 Jorgensen, C. A., 1928. The experimental formation of heteroploid plants in the genus Solanum. J. Genet. 19: 133-211. PA1 Smith, P. G., 1944. Embryo culture of a tomato species hybrid. Proc. Amer. Soc. Hort. Sci. 44: 413-416. PA1 Niles, J. J., 1951. Hybridization methods with paddy. Trop. Agric. Ceylon 107: 25-29. PA1 Honma, S., 1955. A technique for artificial culturing of bean embryos. Proc. Amer. Soc. Hort. Sci. 65: 405-408. PA1 Nishi, S., J. Kawata and M. Toda, 1959. On the breeding of interspecific hybrids between two genomes, "c" and "a", of Brassica through the application of embryo culture techniques. Jap. J. Breed. 8: 215-222. PA1 Harberd, D. J., 1969. A simple effective embryo culture technique for Brassica. Euphytica 18: 425-429. PA1 Fridriksson, S. and J. L. Bolton, 1963. Preliminary report on the culture of alfalfa embryos. Can. J. Bot. 41: 439-440. PA1 Kasha, K. J. and K. N. Kao, 1970. High frequency haploid production in barley (Hordeum vulgare L.). Nature 225: 874-876. PA1 (a) growing Brassica oleracea plants in the planting area which are fully male and female fertile, possess 18 chromosomes, and exhibit cytoplasmic triazine tolerance, PA1 (b) contacting the planting area with triazine in an amount sufficient to substantially destroy broadleaf weeds while maintaining said Brassica oleracea plants substantially intact, and PA1 (c) harvesting the cole crop.
The transfer of resistance to race 2 of Plasmodiophora brassicae from Brassica napus to B. oleracea by Chiang et al. described in the above and subsequent articles is the only known published account of a gene transfer between the species. Accordingly, it has not heretofore been apparent to those skilled in plant technology how one could with certainty transfer triazine tolerance from Brassica campestris or B. napus to B. oleracea to achieve fully fertile plants having the 18 chromosomes characteristic of B. oleracea.
The technique of in vitro culture to rescue inviable interspecific hybrids has been used as early as 1925 to rescue hybrids of Linum perenne and L. austriacum as reported in Laibach, F., "Das Taubwerden von Bastardsamen und die Funstliche Aufzucht fruh absterbender Bastardembryonem", Z. Bot. 17: 417-459 (1925). This technique subsequently has been used to generate both interspecific and intergeneric hybrids in a large number of genera including Solanum, Lycopersicon, Oryza, Phaseolus, Brassica, Medicago, and Hordeum as reported in the following technical articles:
Embryo culture also has been employed to re-synthesize Brassica napus from its two progenitor species B. campestris an B. oleracea as reported by Olsson, G. and S. Ellerstrm, oPolyploidy breeding in Europe. In Tsunoda, S., K. Hinata and C. Gomez-Campo (eds.). Brassica Crops and Wild Allies. Japan Scientific Societies Press, Tokyo. (1980).
Our early research efforts via embryo rescue and regeneration to accomplish the transfer of triazine tolerance without loss of fertility to Brassica oleracea are briefly reported in "The Production of Atrazine-Resistant Brassica napus x B. oleracea Hybrids," Cruciferae Newsletter 10, 87 (November, 1985). No 18 chromosome Brassica oleracea plant was produced during our early research or reported in such article.
It is an object of the present invention to provide an improved process for producing a Brassica oleracea cole crop in the substantial absence of unwanted weeds.
It is an object of the present invention to provide Brassica oleracea seeds which yield fully male and female fertile plants which exhibit cytoplasmic triazine tolerance.
It is an object of the present invention to provide fully male and female fertile Brassica oleracea plants which exhibit triazine tolerance.
It is an object of the present invention to provide an improved process for producing a cole crop wherein the necessity for hand and/or mechanized weed removal is substantially minimized.
It is an object of the present invention to take possible the successful growing of a cole crop in rotation with a corn crop wherein a triazine herbicide was applied to control weeds.
It is another object of the present invention to make possible the successful growing of a cole crop from seeds in the substantial absence of unwanted weeds without the need for substantial hand and/or mechanized weed removal.
It is a further object of the present invention to make possible the successful production of cole crop seeds substantially uncontaminated with other triazine susceptible weed seeds of the Brassicaceae or other plant families without the need for substantial hand and/or mechanized weed removal.
These and other objects, as well as the scope, nature, and utilization of the claimed invention, will be apparent to those skilled in the art from the following detailed description and appended claims.